docs(comments): rewrite comments across all crates to the guidelines

Sweep every first-party crate source (1956 .rs files) to the project comment
guidelines: delete redundant restatements, decorative banners, change
narration, and end-of-line comments; keep and tighten the crucial ones
(invariants, bug rationale, SAFETY blocks, ported-source attribution).

No functional code changed. Every edit is proven comment-only against the
prior tree by a comment-stripping lexer (string/char/raw-string aware) plus a
separate doctest-fence check. Where removing a comment made rustfmt or clippy
want to re-lay-out adjacent code, the minimal triggering comment is restored so
code tokens stay byte-identical.

Gates green: cargo fmt --all --check (0 diffs), cargo check and cargo clippy
--workspace --all-targets (0 warnings).

Adds scripts/check_codegen_comment_guidelines.py — the enforcement gate for
these guidelines (flags banners, end-of-line comments, change narration, and
commented-out code).

crates/common/kigi-tool-runtime/tests/should_list.rs

@@ -77,8 +77,6 @@ impl Tool for NeedsAttachmentTool {
     }
 }
 
-// Tool::should_list (typed)
-
 #[test]
 fn default_returns_true() {
     assert!(Tool::should_list(&AlwaysTool, &ListToolsContext::default()));
@@ -109,8 +107,6 @@ fn reads_custom_extension() {
     assert!(Tool::should_list(&tool, &some));
 }
 
-// ToolDyn blanket forwarding
-
 #[test]
 fn dyn_forwards_default() {
     let tool: ArcTool = Arc::new(AlwaysTool);
@@ -136,8 +132,6 @@ fn arc_dyn_callable() {
     assert!(tool.should_list(&ctx));
 }
 
-// ListToolsContext
-
 #[test]
 fn list_ctx_default_is_empty() {
     let ctx = ListToolsContext::default();
@@ -164,8 +158,6 @@ fn list_ctx_clone_is_independent() {
     assert!(!copy.extensions.contains::<AttachmentCount>());
 }
 
-// TypedExtensions standalone
-
 #[test]
 fn typed_extensions_insert_get_remove() {
     let mut ext = kigi_tool_runtime::TypedExtensions::new();